Abstract

The complete series of the otavite-calcite solid has been synthesized by counter diffusion ofCdClz + CaClz and CaCO] through a column of silica hydrogel. In this system there is a strong preferentialpartitioning of Cd in the solid phase, and only a very narrow range of aqueous phase compositions cancoexist in equilibrium with intermediate solid solutions, i.e., the (Cd, Ca)C03 solid solution tend tocrystallize from aqueous solutions in a bimodal way. At high supersaturations, the range of aqueoussolutions from which intermediate solid solutions can nucleate expands, but the bimodal effect remains.This bimodal behaviour accounts for the development of high gradient composistional zoning andoscillatory zoning during the growth process.